1. Field:
The subject matter disclosed herein relates to data communication systems. In particular, the subject matter disclosed herein relates to transmitting data in an optical transmission medium.
2. Information:
Data transmission in an optical transmission medium such as fiber optic cabling has enabled communication at data rates of 10 gigabits per second and beyond according to data transmission standards set forth in IEEE Std. 802.3ae-2002, Synchronous Optical Network/Synchronous Digital Hierarchy (SONET) protocol as indicated in a set of standards provided by the American National Standards Institute (ANSI T1.105.xx) or Synchronous Digital Hierarchy (SDH) as indicated in a set of recommendations provided by the International Telecommunications Union (e.g., ITU-T G.707, G.708, G.709, G.783 and G.784). To transmit data in the optical transmission medium, a laser device typically modulates an optical signal in response to a data signal.
FIG. 1 shows a schematic diagram of a prior art laser driver circuit 2 to provide power to a laser diode 6. In response to the pulse data signal 4, the laser driver circuit 2 provides a pulse current signal 12 and a nominally fixed bias current (not shown) to the laser diode 6. In response to the pulse current signal 12, the laser diode 6 transmits a light signal 10 having an output power 14. A photodiode 8 measures the output power 14 to be used in evaluating the performance of the laser driver circuit 2 or the laser diode 6.
A slope efficiency typically expresses an efficiency of a laser device in generating an output power in response to an input current signal. For example, a slope efficiency is typically expressed as a measurement of a change in output power of a light signal from a laser device divided by a magnitude of a change in input current signal provided to the laser device to transmit the light signal when the laser device is properly biased. The slope efficiency associated with a particular laser device typically changes as a function of age or operating temperature. Beyond a threshold bias current (generated by a laser driver as a component to a pulse current signal), any additional bias current may result in a diminishing increase in output power. Such a threshold associated with a laser device typically changes over age and operating temperature. For example, FIG. 2 shows a graph illustrating effects of temperature (i.e., different temperatures T1, T2 and T3) on a slope efficiency of a laser device. In the illustrated example, the laser device has a higher slope efficiency at lower operating temperatures.